To best value “Martian Child,” one must stow away any expectation of something fantastical occurring in the story. Part of me wanted the film to take a great leap of faith and assume a controversial, otherworldly stance, daring the audience to believe in the miracle of science fiction. That doesn’t happen. Instead, “Martian Child” has a quality far more earthbound: it’s sweet.

David (John Cusack) is a widower looking toward adoption to start a family. At the agency, he meets Dennis (Bobby Coleman), a withdrawn child who insists he’s a visitor from Mars. David is enthralled by the boy’s imagination and takes on the challenge of raising him, even entertaining the validity of his powers. However, as time passes and Dennis’s psychological ailments show no sign of relenting, David starts to fatigue of the act, and attempts to bring Dennis back into the real world he’s been so stubbornly resisting.

“Martian Child” has so much heart going for it that it occasionally clouds the execution of the film. It’s a well-intended psychological drama, but director Menno Meyjes is too afraid to permit the film any darkness. Instead, “Child” is a patchy creation, bouncing between sincere questions of homestead stability and fluffy sitcom montages set to ELO hits.

Being a family film, perhaps “Martian” shouldn’t even concern itself with gloom, but there’s a yearning to Cusack’s comprehensive performance that pursues uncomfortable ideas of sanity when the film doesn’t dare take a step further. Cusack is the force of energy the rest of “Child” relies on, giving depth to David’s experience with Dennis, never judging or scolding the boy, just simply paralyzed with curiosity. The actor sells the more whimsical moments of the film well, but his true fire is revealed in the moments when Dennis observes his new son. Watching the stardust of possibility shoot through Cusack’s eyes as Dennis goes about his Martian business is a tremendous piece of acting.

The rest of “Child” is lacking that same curiosity, pushing the story through sludgy melodrama as Dennis and David are threatened with separation. It’s material many other, better films have covered and it keeps the extraordinary nature of “Child” asleep when it should be the point of direct concern. While Coleman isn’t much of a child actor (he’s a mop of hair with a strawberry pout underneath), there’s a strange magic between Cusack and the boy that the film ignores in the hunt for mainstream acceptance (not to mention the chance to pile in as much product placement as possible).

Spending his formative years under the tutelage of Steven Spielberg, Meyjes doesn’t use that diamond of experience for the conclusion of “Child;” instead, he employs one idiotic moment of recognition and an extended high altitude confessional to close this story, turning the potential for wonder into a warm, bland hug.